Typical turbine engines for aircraft, such as helicopters, have a compressor, a turbine, a combustion chamber and a fuel management system. The fuel management system adjusts the flow of fuel to the combustion chamber in response to a signal that indicates the revolutions per minute (RPM) at which the engine is operating. For example, as a helicopter begins to take-off from a landing area, the RPM falls from a normal operating RPM because power from the engine is used to move the helicopter. The fuel management system responds by increasing the flow of fuel to the combustion chamber and thereby returns the RPM to normal. Some fuel management systems are operated electrically; others are pneumatic: compressed air is supplied as the power that operates the system. For example, the ALLISON 250-C20 series engine manufactured by General Motors Corporation for use in helicopters is one known engine that uses a pneumatic fuel management system. A pneumatic sense line communicates compressed air from a source, such as the compressor, to the fuel management system. The pneumatic sense line is a metal tube, typically stainless steel, that connects with fittings to a boss on a scroll of the engine. The scroll is a ring-like tube disposed around the output side of the compressor, and the boss is a threaded connector for the pneumatic sense line. Stated in the parlance of the industry, the pneumatic sense lines are pneumatic circuitry that connect to the fuel management system.
The compressor supplies compressed air for use in the combustion chamber. The compressor mounts at a forward portion of the engine and includes a plurality of sets of rotatable and stationary blades. A set of blades is generally referred to as a stage of the compressor. The rotatable blades attach and extend radially outward from a drive shaft and the stationary blades attach to a side wall and extend inwardly. The drive shaft mounts on bearings in the engine and is disposed along the longitudinal axis of the engine. Air enters the intake side of the compressor and passes over and around the blades, while the drive shaft is rotating as discussed below. The blades cooperate to compress the air that passes over the several rotating stages of the compressor. The compressed air exits the compressor and then enters the scroll. A portion of the compressed air flows from the scroll through the pneumatic sense line to the fuel management system. Often the compressed air in the pneumatic sense line is filtered before being communicated to the fuel management system in order to remove particulates and other corrosive materials that are carried in the air through which the aircraft is traveling.
The scroll includes a pair of tubes that extend rearward to communicate the compressed air to the combustion chamber. The compressed air is mixed in the combustion chamber with a combustible fuel and ignited. The resulting burning air/fuel mixture generates gases at high pressures, which gases pass through the turbine and exit through an exhaust. The turbine comprises a plurality of blades that attach and extend radially outwards from a second portion of the drive shaft. The blades often are pitched at an angle to the longitudinal axis of the drive shaft. The force of the gases impacting on the blades cause the drive shaft to rotate at high speed, and thereby turn the compressor blades and a propeller or rotor that attaches at one end of the drive shaft to move the aircraft.
During operation of the aircraft, the fuel management system adjusts the flow of fuel to the combustion chamber. A governor monitors the RPM of the drive shaft in the engine and communicates a signal proportional to the RPM to the fuel management system. In response, the flow of fuel is increased or decreased. For example, a helicopter engine operates at a normal predetermined speed identified as 100% RPM. When the helicopter takes off or moves through the air, the angle of attack for the rotor is changed and additional power is required to maintain the rotor at the 100% RPM. The increased demand for power reduces the RPM of the engine, and in response to the signal from the governor, the fuel management system increases the fuel flow to return the RPM to normal.
The fuel management system includes a body having needles, springs and ports for communicating fuel from a fuel tank to the combustion chamber. The internal body of the fuel management system is primarily aluminum with aluminum parts and castings. The aluminum surfaces are not painted or coated and the aluminum is susceptible to corrosion. The filter discussed above reduces the amount of corrosive materials that pass to the fuel management system, but the corrosive materials that pass through the body attack the aluminum surfaces and create pits thereon as well as leave surface deposits. Corrosion degrades the performance of the fuel management system and may lead to failure of parts in the system. If the fuel management system stops working, or works improperly, fuel will not be supplied to the combustion chamber in the necessary volume to meet the demand for operating the aircraft and the engine may stop operating. This could result in the aircraft crashing.
A bleed valve sense line is another pneumatic sense line typically found on aircraft engines. The bleed valve sense line communicates the static pressure of the compressed air to a bleed valve. The bleed valve opens to release compressed air from the scroll to the atmosphere when the air is compressed to a pressure greater than necessary for the engine to operate. Should the air be excessively compressed, a compressor stall could occur and result in engine shut down. Typically, the air is over compressed only when the aircraft is waiting to takeoff and the engine is operating at 100% RPM. The bleed valve then opens and releases a portion of the compressed air.
Operation of such turbine engines necessarily requires that significant volumes of air pass through the compressor. Such air includes a variety of materials such as dust and dirt particles, smog and other air-borne particulates. For example, coastal areas have high amounts of air-borne salts that are carried into the compressor. During operation of the aircraft engine, such materials tend to deposit and build-up on the blades of the compressor. Over time, such build-up of materials degrades the performance of the compressor and thus degrades the performance of the aircraft engine. Manufacturers of such aircraft engines typically recommend that these materials be routinely washed from the compressor at regular intervals. The blades and the compressor are washed clean with an aqueous solution that is sprayed into the intake side of the compressor. The aqueous solution can be either clean water or a solution of water and a cleaning agent or solvent. For example, the maintenance manual for the ALLISON 250-C20 series engine describes two levels of cleaning procedures for proper maintenance of the compressor. The first cleaning procedure involves rinsing the compressor with the best water available on a daily basis when the engine is operated in a corrosive atmosphere. The second cleaning procedure involves washing the compressor with a solution of an approved aircraft skin cleaner and water. It is suggested that such cleaning is normally required after 200-300 hours of operation in smoggy areas.
The cleaning solution is sprayed into the compressor intake while the engine is motored with the starter without ignition. Preferably, the solution is injected with an aspirator or sprayer equipped with a quick opening valve. It is recommended that the injection start approximately three (3) seconds prior to starter engagement, and the starter is disengaged at ten percent (10%) of the normal operating RPM. Approximately one liter of cleaning solution is injected in about nine to eleven (9-11) seconds, and the engine speed is maintained below ten percent (10%) for the duration of the injection. The injection cycle may be repeated as necessary until the compressor and the blades are cleaned.
When cleaning the compressor with a solvent or other cleaner in the aqueous solution, the bleed valve sense line and the pneumatic sense line first must be disconnected and removed. The fittings are then capped. Removing these lines and capping the fittings prevents the cleaning solution and dislodged materials from entering and contaminating the fuel management system, the bleed valve and the pneumatic sense lines therefor.
Removing the pneumatic sense lines and capping the fittings is a time consuming process. Maintenance personnel working on aircraft engines are highly paid, so the costs for this second cleaning procedure is significantly higher than the costs for the first maintenance procedure. Further, removal and reinstallation of the pneumatic sense lines causes wear on the fittings and the tubes that comprise the pneumatic sense lines. The tube is susceptible to bending, and bends possibly result in cracks, especially beneath the area of the floating ferrule and at the flared ends of the tube. Accordingly, the tube must be carefully inspected for such wear, bends and cracks before the pneumatic sense line is reinstalled. Also, the fittings for the pneumatic sense lines are subject to over-torquing during removal and reinstallation. The pneumatic sense line further may be improperly aligned with the scroll and thereby create a leak at the fitting. Failure to detect such problems with the pneumatic sense line for the fuel management system may lead to failure of this line during operation of the aircraft. As a consequence of such a mechanical failure, the engine would decelerate and could cause an unscheduled landing.
As discussed above, a daily water rinse of the compressor is recommended when operating the engine in a corrosive atmosphere. Often the water rinse is made without disconnecting any of the pneumatic sense lines, in accordance with the procedure specified by the engine manufacturer. The water is sprayed into the rotating compressor as discussed above. The water dislodges materials from the blades, thereby cleaning the compressor. The water droplets with the dislodged materials are carried in the compressed air through the pneumatic sense line and the fuel management system. After completing the rinse, the engine is operated with the igniter on in order to dry the combustion chamber. The compressed air purges the pneumatic sense lines, the fuel management system, and the bleed valve.
The purpose of the daily wash and the cleaning with aircraft skin cleaner is to remove dirt and other materials from the compressor. Without disconnecting the pneumatic sense lines, such materials may accumulate in the pneumatic circuits of the fuel management system and in the bleed valve, which leads to contamination and possible interference with proper operation of the engine. For example, a turbine engine operated in a salt atmosphere, such as in coastal areas, experiences a build-up of salt, among other materials. The wash water spray, as it enters the compressor is clear, but the salt is dissolved and carried with the other materials in the compressor air and water spray through the pneumatic sense line and through the fuel management system. The engine is then operated to dry the combustion chamber and purge the fuel management system. However, crystal deposits may remain in the fuel management system. These salt and other materials are corrosive and begin attacking the smooth surfaces in the fuel management system. However, disconnecting the pneumatic sense lines during the routine daily cleaning increases the wear and tear on the tube that comprises the pneumatic sense line and is time consuming, as discussed above.
Persons operating such aircraft turbine engines accordingly face difficult problems when cleaning the compressor periodically. The cleaning may occur as frequently as each clay, but pursuant to manufacturers' recommendations, cleaning occurs at least every 200 to 300 hours of operation. The manufacturer-specified procedure for cleaning with water only on a daily basis permits the flow of water, salt, dirt and other contaminating materials through the fuel management system. This procedure, however, leaves some surface contamination in the pneumatic sense line and in the body of the fuel management system, resulting in corrosion. The alternative manufacturer-specified procedure for cleaning with water and a cleaning agent requires removal of the pneumatic sense line and capping the fittings on the scroll. This procedure increases the wear on the pneumatic sense line, is time consuming, and more expensive than the first maintenance procedure. Persons involved with maintaining such aircraft engines accordingly must accept some contamination and build up in the fuel management system with resulting corrosion, or accept significantly higher maintenance costs and increased wear on the pneumatic sense lines with the attendant risks of failure during operation of the aircraft.
Accordingly, there exists a need in the art for a convenient, reliable apparatus that closes the pneumatic sense lines and isolates the pneumatic circuitry for the engine fuel management system and the compressor bleed valve to avoid contamination thereof during the routine, periodic washes of the compressor.